In August 2016, astronauts Stephanie Wilson, Karen Nyberg, and Rick Mastracchio (L to R) conducted testing in a model of the Orion spacecraft at the Johnson Space Center to gather the crew's feedback on the design of the docking hatch and on post-landing equipment operations. Orion will eventually carry a crew to Mars. Image credit: NASA
An American space mission to Mars is no longer science fiction; President Obama has pledged to send humans to Mars by 2030. However, NASA-funded research published in Scientific Reports reveals that the tremendous galactic radiation that astronauts will be exposed to causes significant cognitive impairments similar to dementia in rodent models.
To recreate the effects of galactic radiation, “we have to simulate the space radiation environment on Earth, which, as you might imagine, is not a trivial task,” Charles Limoli, a professor of radiation oncology at University of California, Irvine and corresponding author on the study, tells mental_floss.
At the NASA Space Radiation Laboratory (NSRL), part of the Brookhaven National Lab in New York, mice were exposed for a few minutes to charged particle irradiation (ionized oxygen and titanium) similar to those found in the galactic cosmic rays, and then sent back to Limoli’s lab for study. The mice received radiation that approximates the 30 degrees centigray astronauts would receive on a round-trip mission to Mars, including both time spent traveling in space and on the surface of Mars, which does not have a protective magnetosphere, as Earth does.
At 12 and 24 weeks after exposure, researchers studied the neurons in the hippocampus and medial prefrontal cortex of the mice. Healthy neurons have a tree-like structure, with branches known as dendrites and axons that project off the dendrites. A healthy brain has good “dendritic complexity”—or numerous branches. The study found that following exposure to these charged particles, the complexity of this branching pattern deteriorates and, “These branches basically disappear,” says Limoli. They also found that the branch or “spine” density was reduced in those animals exposed to radiation. There was also evidence of neuroinflammation that persisted up to six months after exposure.
Unsurprisingly, “the animals that did the worst on behavioral tasks had the lowest spine density,” he says. Moreover, the results lend creditability to the idea that these changes “probably represent some of the underlying mechanisms for the cognitive impairments we see so long after irradiation,” he says.
These impairments were in learning and memory, elevated anxiety, and trouble in “cognitive flexibility,” a measure of executive function—or the ability to multitask.
While the study was done on mice, Limoli says there’s no evidence to suggest that “a human neuron would respond in any fundamentally different way than a rodent neuron.”
The Mars mission is also unique among space missions because of the time it takes to travel, which limits the number of people who can go. “The astronauts have to work under almost complete autonomy that far out, and their ability to respond to an unanticipated situation, or performance in some mission-critical elements might be impaired,” Limoli says. They might also experience long-term health consequences after returning to Earth.
One of the limitations of the research, Limoli laments, is that the lab simulation doesn’t accurately recreate the galactic cosmic rays that astronauts will be subject to, which include dozens of ions. These rays also “travel very fast and can traverse the whole of the spacecraft and the body of an astronaut,” he says.
As part of NASA’s Human Research Program, he and others are working on simulating the radiation fields in space more effectively, building better shielding technology, and investigating other ways to mitigate damage to the human brain. At the moment, there is no physical shield capable of withstanding galactic cosmic rays. However, Limoli’s lab is working on biological agents that could be taken orally, which he thinks “will be able to both protect the brain and help the brain recover following exposure.”
Regardless of the dire-sounding nature of these results, Limoli stresses, “This isn’t a deal breaker for space travel. It’s something you need to be aware of to develop countermeasures.”